1. Field of Invention
Embodiments of the present invention generally relate to a system for supporting a plurality of hydrocarbon-bearing wells, including systems for providing production operations in multiple-well-site, offshore fields.
2. Description of Related Art
Over the last thirty years, the search for oil and gas offshore has moved into progressively deeper waters. Wells are now commonly drilled at depths of several hundred feet and even several thousand feet below the surface of the ocean. In addition, wells are now being drilled in more remote offshore locations.
Where the water is too deep to establish a foundation on the ocean floor for a production platform, a subsea wellhead may be placed on the ocean bottom. Alternatively, a floating production platform is provided for structurally supporting surface wellheads for wells in deep water. In either configuration, the wellheads will typically physically support concentric tubular pipe strings, such as casing and tubing, with the casing and tubing extending into the well bore. Production fluids may then be directed from a subterranean formation upward through the tubing and to the wellhead. From there, production fluids are delivered by a flow-line to a gathering system.
The drilling and maintenance of deep and remote offshore wells is expensive. In an effort to reduce drilling and maintenance expenses, remote offshore wells are oftentimes drilled in clusters. This allows a single floating rig or semi-submersible vessel to conduct drilling operations from essentially a single ocean location. Further, this facilitates the gathering of production fluids into a local production manifold after completion. Fluids from the clustered wells are oftentimes commingled at the manifold, and delivered together through a single flow-line. The flow line leading from the production manifold is sometimes referred to as a production export line. The clustering of wells also allows for one or more control lines to be run from a single location at the ocean surface, downward to the clustered wells. The control line ties into a control module on the manifold, and then branch to the various wellheads. Such a control line allows for the monitoring and control of valves, gauges, and other subsea equipment. Control lines also allow for one or more power lines or chemical delivery lines to be delivered from the ocean surface, downward to the clustered wells.
A grouping of wells in a clustered subsea arrangement is sometimes referred to as a “well-site.” A well-site typically includes producing wells completed for production at one and oftentimes more pay zones. In addition, a well-site will oftentimes include one or more injection wells to aid production for water drive and gas expansion drive reservoirs. The wells may have “wet” wellheads, that is, the christmas tree is located on the ocean floor (known as a subsea tree or subsea well), or the wells may have “dry” wellheads, meaning that the christmas trees are located on a production platform above the ocean surface. It is desirable to be able to provide an inter well-site controls network by which operations at more than one well-site can be controlled from any of the well-site locations.
It is sometimes necessary to perform intervention services for these wells. Intervention operations involve the transport of a workover vessel to the subsea well-site, and then the running of tools and fluid into the hole for remedial or diagnostic work. Thus, it is also desirable to provide a floating vessel from which intervention services may be provided at one well-site, while utilizing the inter well-site controls network to control operations at that and other well-sites. Additional related information may be found in U.S. Pat. No. 4,052,703 to Collins et al. and GB 2,299,108 to Norske Stats Oljeselskap a.s.